If you are looking for an ethical, environment-friendly holiday, it seems like the perfect place to start. Responsible Travel promises 'hand-picked holidays from hundreds of specialist operators who care about the environment and local people'. The company is by far the most successful of its kind, and has unimpeachable eco-credentials to match - one of the founders was professor of responsible tourism management at Leeds Metropolitan University, early backing came from The Body Shop's Anita Roddick and it organises the high-profile Responsible Tourism Awards.

But when I went on to its website to look for a family skiing holiday, alarm bells began to ring. One holiday was a week's trip to Whistler, on Canada's west coast. To get there, you fly to Vancouver, and in doing so will emit 2.14 tonnes of CO2 per person, at least 11 times the amount emitted on a flight to Geneva, from where a huge range of equally good resorts can be reached.

In fact, five of the 23 skiing holidays Responsible Travel had 'hand-picked' are in Canada, two are in Japan and a total of nine involve long-haul flying. It's not as if the firm isn't conscious of the flying issue. Writing recently in the Daily Telegraph, its chief executive and co-founder, Justin Francis, said: 'At Responsible Travel, we believe that we must fly less each year, for example by taking holidays closer to home and travelling by train.'

Of course, flying long-haul is inherent in many trips which aim to support poor communities in developing countries, but Whistler is a vast, purpose-built resort owned by Intrawest, a huge corporation that develops golf and skiing resorts around the globe and owns the world's biggest heli-skiing firm. In recent years it has been turning its attention to Europe and is working on plans to develop the sleepy Swiss village of Bruson, despite opposition from the WWF, which fears that new lifts, runs and apartment complexes will destroy the natural environment.

Alarms bells rang louder still when I discovered who was actually behind the trip. Responsible Travel doesn't run holidays itself, it just works as an agent. After you register your interest, you get an email from your 'specialist tour operator' which, the website assures you, will be run by 'passionate people who care about the environment'. My email comes from Neilson - the skiing and sailing division of Thomas Cook. Thomas Cook, as in the second-largest travel company in Europe, with 97 aircraft, 2,926 high street shops, 32,722 employees and more than 19.1 million annual customers. A small specialist ethical travel firm, it is not.

In fact, cash-strapped eco-tourism businesses are less likely to find their way onto responsibletravel.com, because (apart from a tiny number of community-run projects) everyone has to pay a fee to be featured. They then also pay a commission - typically 7 per cent of the holiday price.

'The issue I have is that a commercial travel agent has appropriated the name "responsible travel" and by so doing gives the appearance of being an official industry portal to find those kind of trips,' says Roger Diski, founder of Rainbow Tours, a specialist African tour operator. 'But they charge operators to be on the site, which means that only those who are prepared to pay them commission on sales are on there. Furthermore, monitoring of standards is rudimentary; much of what is on there has no particular claim to be responsible.'

Justin Francis responded to our concerns by saying that his site featured large numbers of UK and short-haul holidays. Some people, he argued, would have already decided to go to North America, and using Whistler, which has won awards for environmental policies including encouraging staff to car-share, recycling and reducing waste, would be better than sending them to other Canadian resorts. The phrase 'specialist operators' was not intended to imply the holiday companies featured were specialists in responsible travel, rather that they were specialists in the type of holiday offered, in this case skiing, who also had a responsible travel policy.

And yet no one could argue that flying around the globe to a purpose-built resort was greener, more responsible or more ethical than taking a train to the Alps and staying in a locally owned hotel in a small community. And if this company, which is at the heart of the British ethical tourism movement and whose boss regularly lectures on the subject, isn't beyond reproach, what can we expect from the rest of the industry?

Suddenly, it seems that every hotel, tour operator and even airline is bending over backwards to do its bit for the planet. Adverts and websites are full of claims about the good that choosing a particular holiday will do for the environment and local communities. And amid such a profusion of green claims, it's becoming increasingly hard to tell who is genuinely concerned about the planet and who is just cashing in on our eco-guilt.

'Already the word "eco" has lost all power and meaning,' says Guyonne James, senior projects manager at Tourism Concern, a UK charity which campaigns against exploitation. 'In Brazil, if a bed-and-breakfast has a back garden, they'll call it an eco-lodge. There has been such a proliferation of claims and green labels that as a tourist you really have no idea what's going on.'

Sometimes 'greenwashing' - dressing something up to appear more ethical, sustainable and hence saleable - is a cynical ploy; in other cases, it's simply the result of a well-meaning organisation getting slightly carried away. The Austrian tourist authorities, for example, do a huge amount of work to promote responsible travel, but last month went over the top when they launched a publicity campaign telling travellers they could 'reduce their carbon footprint' by going on holiday to the country.

'Staying in one of Austria's leading environmentally friendly resorts could in some cases cause fewer carbon dioxide emissions than staying at home in the UK,' said the publicity, though it didn't explain how this miracle was possible. 'Unless you cycle there, I can't see any way this would work,' said Charlie Kronick, Greenpeace's carbon campaigner, when we put the claim to him.

In Britain, the Advertising Standards Authority (ASA) is reporting a boom in the number of complaints about environmental claims - up from 117 in 2006 to 561 last year. 'What we are seeing is claims about being carbon-neutral, zero-carbon emissions and use of words such as "sustainable", "organic",' says Lord Smith, chairman of the ASA. 'Many are exaggerated or misleading.'

Examples of greenwashing extend right across the travel industry, from a tiny family-run boat trip business on Skye, which was censured by the ASA for claiming its boat was 'friendly to the environment and wildlife', to giants such as Boeing, which was criticised for overstating the environmental credentials of its latest 747 in an ad headlined 'Our commitment to a better future'.

Easyjet has come in for criticism several times, most recently last week. In an advert entitled 'Demand a more intelligent approach to aviation', it claimed it emitted 22 per cent less carbon dioxide than traditional airlines. The ASA upheld a complaint and called the ad misleading. Even local authorities can get carried away. Devon got into trouble for an advert headlined 'The perfect answer to global warming? Devon chillin',' in which it claimed it was 'England's greenest county'. The ASA said the council had no evidence to back this up.

'Greenwash is the spanner in the works that could sabotage the whole environmental movement within business,' says Solitaire Townsend, chief executive of Futerra, a consultancy that publishes a report called The Greenwash Guide. 'Greenwash means that confidence in green advertising is at an all-time low, and if consumers can't believe the claims they won't buy the products and the good will lose along with the bad.'

In some cases greenwashing can result from the travel industry's long 'supply chains'. A British operator will often subcontract to a 'ground handler' in the destination country, which will use a variety of accommodation suppliers, guides and excursion providers, all from separate companies. For the British tour operator, finding out detailed environmental information about the end suppliers is a daunting task.

In May, Escape reader Jamie Bennett and his wife, Susan, took a three-week trip to Brazil, Bolivia and Peru with tour operator Explore, which included wildlife watching in Brazil's Pantanal wetlands. Explore, which has won awards for its approach to responsible travel, has stringent policies about wildlife, right down to avoiding using a flash when photographing animals. 'We were shocked to find we were housed on a cayman farm, where these small alligators were battery farmed for their skins,' says Jamie. 'The farm had pelts draped over the furniture, alligator-skin key fobs and cayman meat at every meal. Up to 200 animals were held in small concrete pens with no natural light. As vegetarians who are opposed to the exotic animal skin trade, we were deeply disturbed to be supporting the trade financially.'

Explore explained to the Bennetts that it had been told by the lodge's owner that cayman farming was positive because it caused a reduction in poaching. 'We rely on information given to us by our local agents and suppliers,' wrote Ashley Toft, Explore's managing director. 'As it is not feasible for us to directly verify every piece of information received, there has to be an element of trust in our relationship with our suppliers.'

Understandable enough, but it throws a slightly different perspective on Explore's promise on its website: 'We audit every single one of our tours for its responsible tourism credentials. All aspects of tours are considered, from the use of fuel to transport options, treatment of animals and our positive impacts on the local economy.'

Last week, Explore told us that it neither supports nor opposes cayman farming and the skin trade, but recognises this is a sensitive issue. It was aware the lodge was part of a cayman farm, but stresses the owner is a vet who takes welfare seriously.

In reality, there is a sliding scale of green, from hotels that do little more than ask you to reuse towels, to those that provide renewable energy for heating and electricity, recycle religiously, grow their own food and offer discounts if you arrive by public transport.

Rosehill Lodges in Porthtowan, Cornwall, which boasts that its lodges are 'built to the highest environmental standards', is somewhere in between. The eight grass-roofed lodges are heavily insulated, the walls are made of larch certified by the Forestry Stewardship Council, the floors are from sustainable sources of bamboo and there's solar heating for the showers. Yet each lodge has a large, energy-guzzling hot tub, which may be good for aching limbs but is not so kind to the planet. The tubs require electric heating, gallons of chlorinated water and frequent maintenance. So should the business be lambasted for greenwashing or praised for everything it's doing right?

Tourism Concern points to a more extreme example. Hilton Hotels recently announced a string of laudable initiatives to reduce water use, but it is also opening a new luxury resort on Bimini Island in the Bahamas, part of a huge development which the charity claim is causing devastating environmental damage. 'We have to give credit where it's due, but at the same time, you have to look at the bigger picture, and one responsible policy should not be used as a fig leaf to hide behind,' says Rachel Noble, Tourism Concern's campaigns officer.

So how do you go about working out what is or isn't a responsible trip? In the UK alone, there are more than 20 accommodation eco-labels - including Green Leaf (New Forest), Green Acorn (Cornwall), Green Island (Isle of Wight) - all designed to tell tourists at a glance that they're dealing with a green business. Worldwide, there are more than 100 independent labels, a bewildering mixture of regional, national and international schemes, some of which are commercial while others are run by not-for-profit organisations. Yet there is no international body responsible for regulating them.

However, we are now beginning to see the first moves towards a more transparent system of external auditing. VisitBritain has invited the various eco-labels in the UK to apply to be vetted by Xavier Font, a specialist in responsible tourism certification at Leeds Metropolitan University. 'We wanted to provide clarity not just for hotel and B&B owners on which schemes to select, but also for consumers to know what to trust,' says Jason Freezer, sustainable tourism manager at VisitBritain.

So far the Green Tourism Business Scheme (GTBS) is the only UK eco-label scheme to have successfully completed the vetting procedure. It sends a trained auditor out to each business to check more than 150 criteria, from energy and water conservation to how food and supplies are sourced. Most of its accredited businesses are small firms, but now the big package companies are also making moves in the right direction. The Federation of Tour Operators, whose members carry around 18 million UK travellers annually, has developed a common environmental standard for its members' hotels, known as the Travelife Sustainability System. First Choice, Virgin Holidays and Thomas Cook have already introduced the Travelife logos in their brochures to flag up green hotels, all of which will have been visited by a trained sustainability auditor.

'Ironically, it could be the big tour operators rather than the small specialists who end up taking the lead in this,' says John Swarbrooke, head of the Centre for International Tourism Research at Sheffield Hallam University. 'They are coming under great pressure from shareholders to make sure they are seen to take this seriously, and in turn they have the power to make sure all their suppliers on the ground take action.'

But perhaps the biggest step towards common standards could come later this year. Fairtrade Labelling International (FLI), the umbrella body behind the Fairtrade label for food products, is carrying out a feasibility study into a global Fairtrade label for tourism, and expects to reach a decision by the end of the year. Concerns have been raised about the complexity of the tourism industry, but others point out that global food supply chains can be equally convoluted. 'Fairtrade is one of the few labels that people around the world trust,' says Guyonne James at Tourism Concern, which is working with FLI on its study.

Until then, the only real solution is to ask lots of questions of your tour operator, travel agent or hotelier and carry out your own research rather than trusting that a labelling scheme or a particular company will do it for you. How many people will take the trouble to do this is another matter.

'Without a credible labelling system, there's a very real danger now that we'll have a backlash and that tourists will just get cynical,' says Swarbrooke. 'Lots of people want to do the right thing, but without any guidance they'll just throw their hands in the air and stop bothering about responsible travel altogether.'